Add missing build time class initialization

As spring-projectsgh-28624 supports only static boolean fields, we still
need a few classes to be initialized at build time.

Such explicit configuration should be in theory avoidable,
so we will work with the GraalVM team to see if this can be
fixed, see for example
oracle/graal#4673
for HttpStatus.

See spring-projectsgh-28624

Author: sdeleuze

spring-core/graalvm/src/main/resources/META-INF/native-image/org.springframework/spring-core/native-image.properties

@@ -0,0 +1,5 @@
+Args = --initialize-at-build-time=org.springframework.aot.graalvm.ThrowawayClassLoader,\
+org.springframework.util.ClassUtils,\
+org.springframework.util.ConcurrentReferenceHashMap,\
+org.springframework.util.MimeType,\
+org.springframework.util.MimeTypeUtils

spring-core/src/main/resources/META-INF/native-image/org.springframework/spring-core/native-image.properties

@@ -0,0 +1,2 @@
+Args = --initialize-at-build-time=org.springframework.http.HttpStatus,\
+org.springframework.http.MediaType